Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional vacuum IG unit (vacuum IG unit or VIG unit). Vacuum IG unit 1 includes two spaced apart glass substrates 2 and 3, which enclose an evacuated or low pressure space 6 therebetween. Glass sheets/substrates 2 and 3 are interconnected by peripheral or edge seal of fused solder glass 4 and an array of support pillars or spacers 5.
Pump out tube 8 is hermetically sealed by solder glass 9 to an aperture or hole 10 which passes from an interior surface of glass sheet 2 to the bottom of recess 11 in the exterior face of sheet 2. A vacuum is attached to pump out tube 8 so that the interior cavity between substrates 2 and 3 can be evacuated to create a low pressure area or space 6. After evacuation, tube 8 is melted to seal the vacuum. Recess 11 retains sealed tube 8. Optionally, a chemical getter 12 may be included within recess 13.
Conventional vacuum IG units, with their fused solder glass peripheral seals 4, have been manufactured as follows. Glass frit in a solution (ultimately to form solder glass edge seal 4) is initially deposited around the periphery of substrate 2. The other substrate 3 is brought down over top of substrate 2 so as to sandwich spacers 5 and the glass frit/solution therebetween. The entire assembly including sheets 2, 3, the spacers, and the seal material is then heated to a temperature of approximately 500° C., at which point the glass frit melts, wets the surfaces of the glass sheets 2, 3, and ultimately forms hermetic peripheral or edge seal 4. This approximately 500° C. temperature is maintained for from about one to eight hours. After formation of the peripheral/edge seal 4 and the seal around tube 8, the assembly is cooled to room temperature. It is noted that column 2 of U.S. Pat. No. 5,664,395 states that a conventional vacuum IG processing temperature is approximately 500° C. for one hour. Inventors Lenzen, Turner and Collins of the '395 patent have stated that “the edge seal process is currently quite slow: typically the temperature of the sample is increased at 200° C. per hour, and held for one hour at a constant value ranging from 430° C. and 530° C. depending on the solder glass composition.” After formation of edge seal 4, a vacuum is drawn via the tube to form low pressure space 6.
Unfortunately, the aforesaid high temperatures and long heating times of the entire assembly utilized in the formulation of edge seal 4 are undesirable, especially when it is desired to use a heat strengthened or tempered glass substrate(s) 2, 3 in the vacuum IG unit. As shown in FIGS. 3-4, tempered glass loses temper strength upon exposure to high temperatures as a function of heating time. Moreover, such high processing temperatures may adversely affect certain low-E coating(s) that may be applied to one or both of the glass substrates in certain instances.
FIG. 3 is a graph illustrating how fully thermally tempered plate glass loses original temper upon exposure to different temperatures for different periods of time, where the original center tension stress is 3,200 MU per inch. The x-axis in FIG. 3 is exponentially representative of time in hours (from 1 to 1,000 hours), while the y-axis is indicative of the percentage of original temper strength remaining after heat exposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis in FIG. 4 extends from zero to one hour exponentially.
Seven different curves are illustrated in FIG. 3, each indicative of a different temperature exposure in degrees Fahrenheit (° F.). The different curves/lines are 400° F. (across the top of the FIG. 3 graph), 500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottom curve of the FIG. 3 graph). A temperature of 900° C. is equivalent to approximately 482° C., which is within the range utilized for forming the aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2. Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled by reference number 18. As shown, only 20% of the original temper strength remains after one hour at this temperature (900° F. or 482° C.). Such a significant loss (i.e., 80% loss) of temper strength is of course undesirable.
In FIGS. 3-4, it is noted that much better temper strength remains in a thermally tempered sheet when it is heated to a temperature of 800° F. (about 428° C.) for one hour as opposed to 900° F. for one hour. Such a glass sheet retains about 70% of its original temper strength after one hour at 800° F., which is significantly better than the less than 20% when at 900° F. for the same period of time.
Another advantage associated with not heating up the entire unit for too long is that lower temperature pillar materials may then be used. This may or may not be desirable in some instances.
Even when non-tempered glass substrates are used, the high temperatures applied to the entire VIG assembly may soften the glass or introduce stresses, and partial heating may introduce more stress. These stresses may increase the likelihood of deformation of the glass and/or breakage.
Moreover, the ceramic or solder glass edge seals of conventional VIG units tend to be brittle and prone to cracking and/or breakage, reducing the ability of individual glass panels to move relative to one another. Glass panel movement is known to occur under normal conditions such as, for example, when two hermetically sealed glass components (such as in a VIG unit) are installed as a component of a window, skylight or door, whereby the VIG unit is exposed to direct sunlight and one glass panel has higher thermal absorption than the other panel or there is a great difference between the interior and exterior temperatures.
FIG. 5 is an example conventional VIG unit. In the FIG. 5 VIG unit, first and second glass substrates 2 and 3 with flat edges are used, with the first substrate 2 being slightly smaller than the second substrate 3. The offset typically is about 3-4 mm around the glass perimeter. This design allows the glass frit 4 to be easily applied to the edges in an open environment. The bonding between the frit 4 and the first substrate 2 mainly occurs on two surfaces, namely, the lower surface 2a and the side surface 2b of the first substrate 2. There also is some bonding on the small seamed surface 2c at the corner of the first substrate 2. The slanting main body portion 4a of the glass frit 4 helps retain the frit effectively, with a portion 4b of the frit being allowed to flow into the gap 6 between the first and second substrates 2, 3 by capillary force. Unfortunately, the weight is loaded on the larger second substrate 3 when the unit is installed vertically, putting the larger second substrate 3 under a higher stress in comparison to the VIG unit designs where equally-sized substrates are used. In addition, when the frit is in a small capillary, the edge seal tends be narrow and thus weak.
Chinese Patent Application No. 95108228.0B (which is hereby incorporated herein by reference) discloses several equal-size substrate designs. For example, in FIG. 6, the first and second substrates are equally sized. The second substrate 3 has a flat inner surface 3a, whereas the first substrate 2 has an angled end portion 2c. The FIG. 6 design is desirable from aesthetic and stress loading points of view. As in the offset design described above, the frit 4 flows between the first and second substrates 2, 3 by capillary force. However, when the capillary is small, the edge seal will be formed generally on only a single surface.
FIGS. 7-8 show yet further prior art VIG edge seal designs. For example, FIG. 7 shows a VIG unit having angled top and bottom substrates 2, 3, while FIG. 8 shows a VIG unit having rounded top and bottom substrates 2, 3. In both cases, it would be difficult to retain the frit 4 unless some additional techniques are used to hold the molten frit in place, e.g., during the firing process.
In view of the above, it will be appreciated that there is a need in the art for a vacuum IG unit, and corresponding method of making the same, where a structurally sound hermetic edge seal may be provided between opposing glass sheets. There also exists a need in the art for a vacuum IG unit including tempered glass sheets, wherein the peripheral seal is formed such that the glass sheets retain more of their original temper strength than with a conventional vacuum IG manufacturing technique where the entire unit is heated in order to form a solder glass edge seal.
Certain example embodiments of this invention relate to a vacuum insulated glass (VIG) unit. First and second substantially parallel spaced apart substrates are provided. The first and second substrates form a cavity therebetween. An edge seal is located around the periphery of the first and second substrates. The first substrate, when viewed along a side cross-section, comprises a body portion. A step portion extends a step height H into the cavity from a major axis of the body portion, with an outer edge of the step portion being setback at least a setback distance S from an outer edge of the VIG unit. At least one protrusion extends from the minor axis of the body portion towards one edge of the VIG unit, with the length of the protrusion corresponding to the setback distance S.
Certain example embodiments of this invention relate to a vacuum insulated glass (VIG) unit. First and second substantially parallel spaced apart substrates are provided. The first and second substrates form a cavity therebetween. An edge seal is located around the periphery of the first and second substrates. The first substrate, when viewed along a side cross-section, comprises a first body portion. A first step portion extends a height H1 into the cavity from a major axis of the first body portion, with an outer edge of the first step portion being setback at least a setback distance S1 from an outer edge of the VIG unit. At least one first protrusion extends from the minor axis of the first body portion towards one edge of the VIG unit, with the length of the first protrusion corresponding to the setback distance S1. The second substrate, when viewed from along a side cross-section, comprises a second body portion. A second step portion extends a height H2 into the cavity from a major axis of the second body portion, with an outer edge of the second step portion being setback at least a setback distance S2 from an outer edge of the VIG unit. At least one second protrusion extends from the minor axis of the second body portion towards one edge of the VIG unit, with the length of the second protrusion corresponding to the setback distance S2.
Certain example embodiments of this invention relate to a glass substrate for use in a VIG unit, comprising inner and outer substantially planar surfaces. When considered along a side cross-section, a portion of the inner planar surface is removed proximate to an outer edge of the glass substrate so as to form a shoulder portion. An inner surface of the shoulder portion is angled relative to the inner and outer planar surfaces. The shoulder portion at its smallest height is at least about 50% of the glass substrate at its largest height.
Certain example embodiments of this invention relate to a method of making a vacuum insulated glass (VIG) unit. First and second glass substrates comprising respective inner and outer substantially planar surfaces are provided. When the first and/or second substrates are considered along side cross-section(s), a portion of the inner planar surface is removed proximate to an outer edge of the glass substrate so as to form a shoulder portion, an inner surface of the shoulder portion is angled relative to the inner and outer planar surfaces, and the shoulder portion at its smallest height is at least about 50% of the glass substrate at its largest height. Edges of the first and second substrates are sealed using a frit material in making the VIG unit.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.